Raman study on lead halo borate glasses: Effect of PbO as modifier

摘要

Glasses with xPbX·(30-x)PbO·70B_2O_3 composition (where X=F_2, Cl_2 and Br_2) have been prepared and investigated by Raman spectroscopy with a view to understand the effect of PbO as modifier. The micro Raman spectrum was recorded on Raman spectrometer at room temperature. At high PbO content, Pb enters the glass network as network former, the present investigation deals with modifier role of PbO at low concentration. The measured density values are increasing with increase of PbF_2 content which is due to replacement of relatively lower ionic radii of fluorine ions (1.33A) with oxygen ions (1.4A) and decreasing with PbCl_2/PbBr_2 content which is attributed to replacement of higher ionic radii of chlorine (1.81A)/bromide (1.96A) ions with lower ionic radii of oxygen ions (1.4A). Deconvoluted Raman spectra are used to extract exact band positions. The band positions unveiled that the glass structure is mainly based on trigonal and tetragonal borate units placed in various structural groups. Low concentration of PbO in glass resulted in conversion of boroxol rings into several borate groups, symmetric breathing vibrations of six-member rings with one or two BO_3 triangles replaced by BO_4~- tetrahedral. Raman spectra confirm the presence of Pb ions exists mainly as PbO_4 groups.